Noncovalent Strategy with Cell-Penetrating Peptides to Facilitate the Brain Delivery of Insulin through the Blood-Brain Barrier.

To overcome the difficulty in delivery of biopharmaceuticals such as peptides and proteins to the brain, several approaches combining the ligands and antibodies targeting the blood-brain barrier (BBB) have been tried. However, these are inefficient in terms of their permeability through the BBB and structural modification of bioactive drugs. In the present study, we therefore examined the usefulness of a noncovalent method using the cell-penetrating peptides (CPPs) such as octaarginine (R8) as a suitable brain delivery strategy for biopharmaceuticals. A safety examination using microvascular endothelial model bEnd.3 cells clarified that R8 was the safest among the CPPs tested in this study. The cellular uptake study demonstrated that coincubation with R8 enhanced the uptake of model peptide drug insulin by bEnd.3 cells in a concentration-dependent and a temperature-independent manner. Furthermore, an in vivo study with rats showed that the accumulation of insulin in the deeper region of the brain, i.e., hippocampus, significantly increased after the intravenous coadministration of insulin with D-R8 without altering the insulin disposition in plasma. Thus, the present study provided the first evidence suggesting that the noncovalent method with CPPs is one of the strategic options for brain delivery of biopharmaceuticals via intravenous injection.

Effect of an Enhanced Nose-to-Brain Delivery of Insulin on Mild and Progressive Memory Loss in the Senescence-Accelerated Mouse.

Insulin is now considered to be a new drug candidate for treating dementias, such as Alzheimer's disease, whose pathologies are linked to insulin resistance in the brain. Our recent work has clarified that a noncovalent strategy involving cell-penetrating peptides (CPPs) can increase the direct transport of insulin from the nasal cavity into the brain parenchyma. The present study aimed to determine whether the brain insulin level increased by intranasal coadministration of insulin with the CPP penetratin has potential for treating dementia. The pharmacological actions of insulin were investigated at different stages of memory impairment using a senescence-accelerated mouse-prone 8 (SAMP8) model. The results of spatial learning tests suggested that chronic intranasal administration of insulin with l-penetratin to SAMP8 slowed the progression of memory loss in the early stage of memory impairment. However, contrary to expectations, this strategy using penetratin was ineffective in recovering the severe cognitive dysfunction in the progressive stage, which involves brain accumulation of amyloid ß (Aß). Immunohistological examination of hippocampal regions of samples from SAMP8 in the progressive stage suggested that accelerated nose-to-brain insulin delivery had a partial neuroprotective function but unexpectedly increased Aß plaque deposition in the hippocampus. These findings suggest that the efficient nose-to-brain delivery of insulin combined with noncovalent CPP strategy has different effects on dementia during the mild and progressive stages of cognitive dysfunction.